What I want to achieve is simple:
I'm just answering for someone who has the same problem and found this topic.
I added a permission to Everyone (in this case, it would be in the folder C:\InetPub\my-site\foo\
). Then I printed on the page what user is executing the app in this folder...
Something like:
labelCurrentUser.Text = System.Security.Principal.WindowsIdentity.GetCurrent().Name;
Then I removed the permission to everyone and added the user that I got.